Echo Cancellation in Connect

The best method is muting the mic or using headsets. If this is not possible there is an option of using an echo cancellation software‌ like SoliCall Pro. This software is good for windows platform. Basically it is adding a virtual audio device in which it can do the audio filtering.

Not really. You can play with the Microphone settings and see if you can find a setting that works, probably start with full-duplex and try using the Speex codec.

If you can't get that to work, and can't get the attendees to mute their mic when they are not talking, you may need to look at using headsets or USB speakerphones (which have hardware based duplexing).